An interactive voice call requires transmissions of audio information in both directions between two call termination points. VoIP telephone connections often exhibit large and significant differences in one way delay in the two directions of transmission for a voice call. The VoIP speech signals are typically coded, decoded, and buffered by different network elements in each direction. Dissimilar packet routing and misbehaving network elements can also contribute to the differences in one way delay in different directions of a call connection. A common practice used to calculate one way delay is to measure the round trip delay, assuming the delays in the two directions are equal, and to divide the round trip delay by two. For the reasons stated above, this method often provides inaccurate one way connection delay measurements within VoIP networks.
Even though it is possible to measure the delay in each direction if synchronized test equipment is present at both call termination points of a call connection, this may be practical only if both ends of the connection are present at a single location or collocated. If the two call terminating points are not collocated, test equipment capable of playing and recording test audio files and additional testing personnel would need to be deployed to both call terminating points. This incurs significant costs associated with the field workforce and equipment transport under this type of testing arrangement.